Electrolytic process for the extraction of metallic manganese



June 7, 1938. s. M. SHELTON 2,119,560

ELECTROLYTIC PROCESS FOR THE EXTRACTION OF METALLIC MANGANESE Filed Sept. 10, 1936 Mwafiese Coniaz'ner:

Parifgipp @mm 5 Q n n $0M; M Z H r 6% I Z 5 v Patented June 7, 1938 PATENT OFFICE ELECTROLYTIC PROCESS FOR THE EX- TRACTION OF METALLIC MANGANESE Stephen M. Shelton,

Reno, -Nev., assignor to Government of the United States as represented by the Secretary of the Interior Application September 10, 1936, Serial No. 100,131

13 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention described hereinmay be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention generically relates to the elec-' tro-chemical production of metallic manganese, more specifically it is directed to an improved cyclic process for electrolytically extracting metallic manganese from aqueous solutions.

One object of this invention is to provide a closed cycle process for effecting electro-deposits of substantially pure metallic manganese wherein the partially spent electrolyte in the course of its cycle is rejuvenated with a metallic salt, subsequently purified and then returned to the electrolytical cell in its original state of manganese concentration.

Another object of this invention is to provide a cyclic process of the character described wherein the sulphate ions are continuously or intermittently replaced by sulphite ions to prolong the useful life of the electrolyte, improve the purity of the manganese deposit and control the rate of formation of manganese oxide and hydrates on the anodes and in the electrolyte.

Another object of this invention is to provide a cyclic process for the electro-cleposit of a metallic manganese wherein the rate of flow of the electrolyte and the total volume are adjusted so that ample time will be allowed for reaction between suspended manganese carbonate or oxide on the partially spent electrolyte containing free sulphuric acid.

Another object of this invention is,to provide a manganese extraction process wherein the.

manganese rate or deposit is maintained at a high level to controlthe formation of rough or nodular deposits or the growth of trees"-around the edges of the cathode, both of which reduce the rate of deposition to zero.

Other objects of this invention are to provide a process affording a high degree of current deficiency and one by which a yield of substantially pure metallic manganese is obtained which here tofore has been unattainable. With these and other objects-in view this invention consists of certain noveldetails of construction, combination and arrangement of parts to be more particularly hereinafter described and claimed.

According to the present invention an electrolyte composed of a soluble manganese salt flows through the catholyte compartment of an electrolytical cell, then through its anolyte'compartment and flowing from the latter, the partially spent electrolyte enters a mixing tank where it 'is impregnated with a manganese salt. After rejuvenation in the mixing tank the electrolyte is conducted to a settling or filtering tank for purification and then returned in its initial condition to the catholyte compartment of the cell, the entrance of which is suitably connected with a source of sulphite ion adapted to be continuously or intermittently added in small quantities to the electrolyte.

Referring more particularly to the accompanying drawing in which corresponding parts are indicated by similar reference characters:

The figure is a diagrammatic view illustrating an electrolytic manganese flow sheet and showing one unit of an electrolytical cell, the association and connection of the various tanks connected with it and thefiow of the electrolyte.

Low operating efliciency and impure deposits are largely responsible for the non-utilization by industry of the available methods for electrochemically producingmetallic manganese, For instance Allmand and Campbell, experimentin in this field confirmed the observation of earlier research workers, that the deposition of manganese ceases with solutions containing as high as 0.36 percent sulphuric acid. It was also found that manganese of a high degree of purity could be prepared in small amounts by using a'catholyte containing 300 grams manganous sulphate tetrahydrate, 100 grams ammonium sulphate and 2.5 grams sulphuric acid per liter, the acidity being maintained by suitable additions of acid. Using a rotating cathode, current efiiciencies'of to 60 percent were obtained, using a standard electrolyte of ammonium and manganous sulthat the best conditions for the electrodeposition of manganese were obtained with a catholyte containing manganese and ammonium sulphates, separated by a diaphragm from an anolyte of concentrated ammonium sulphate solution. The pH was kept between 6 and 8 by additions of sulphuric acid or ammonia. The temperature was under the most favorable conditions with a neutral or weakly acid 6.5 normal solution of manganous chloride, at 50 C and a current density of 186 amperes per square foot, the deposit on a copper cathode contained about 65 percent manganese and percent hydrated oxide. Cathode deposits as high as 50 grams were obtained. The influence of the various factors on the purity of the deposit from a sulphate solution was found to be of the same general character as with the chloride solution. Freshly precipitated manganous carbonate was continuously added to neutralize the electrolyte. Experiments on a large scale gave unpromising results.

These findings indicating the state of the art, clearly show availing methods'have serious limitations, in that none of them are suitable for continuous operation for the commercial electrodeposition of manganese as a step in producing manganese from ores or other chemical comis deposited and that no provision is made for control of the tendency to form rough or nodular deposits andto grow trees around the edges of the cathode, which is usually present, and

which gradually reduces the rate of deposition .to zero.

of single manganese deposits producedv electro- Moreover, there is no previous record lytically which weighed more than 50 grams.

With these limitations in view extensive investigations were made and as a result, it has been found that: provided the initial concentration of manganese in the solution is greater than 0.5 gram per liter of manganeseand provided the concentration ratio of ammonium salt, such as ammonium chloride, or ammonium sulphate, to manganese salt, such as manganese chloride or manganese sulphate, measured by normal weight concentration, is one to two, or greater, gray metallic manganese can be deposited at minimum. cathode current densities of 10 amperes more or less, contained 99.6 to 99.9 percent man- .ganese. The deposits .were coherent, compact,

bright metallic, and showed no tendency to grow trees" after a period as long as required for a 72 hour deposition.

Pervious separators or diaphragms, separating the catholyte from the anolyte, such as feltcloth, commercial storage-battery-separators of wood, sheet asbestos-or prepared electrolytic diaphragms of clay, prolong the useful life of a stationary electrolyte and are practically indispensable with a circulating electrolyte. Satisfactory deposits of manganese can be obtained within the concentration limits given at current densities above 10 amperes per square foot within thev acidity range of pH 4.5 to pH 8.5.

For example, deposits purity.

a lases With the preceding facts established, the in- 'stant process wasdevised for producing electrolytic manganese-deposits of high purity and without seriously affecting the usefulness of the circulating "electrolyte during long periods of operation, which will now be explained in detail.

Referring to the flow sheet, the figure of the drawing, A indicates one unit of an electrolytical cell, (a) a cathode located intermediate the two anodes (b), and.(c) the, diaphragms separating the catholyte compartment (d) from the anolyte compartment (e)-.

With this arrangement an electrolyte composed of a suitable manganese salt, ammonium sulphate or ammonium chloride and water, en-' tering the catholyte compartment (d), flows through said compartment to the anolyte compartmentie) and then passes through suitable conduits to a mixing tank, or tanks B in which the partially spent electrolyte is stirred with an excess, of manganese carbonate or lower oxideof manganese (MnO), which is added from the excess manganese carbonate or oxide carried over is partially or completely removed from the electrolyte. After this treatment the electrolyte, reasonably free of Suspended matter is returned to the catholyte compartment (d), whereupon the cycle just described is repeated.

The rate of fiow of the electrolyte and the total volume are adjusted so that ampletime is allowed for reaction between suspended manganese carbonate or oxide and the partially spent electrolyte containing free sulphuric acid. During the cycle described by the electrolyte, a sulphite ion is added continuously, orirom time to time, from tank E to the catholyte compartment (d) of the cell, the sulphite ion being in the form of ammonium sulphite sulphur dioxide gas or sulphurous acid and serves to replace the amount oxidized to sulphate ion. Manife'stly the formation of additional sulphite ion by this treatment will gradually build up the concentration of manganese sulphate in the electrolyte,

" but the rate of addition is relatively so slow that it can be controlled by occasional bleeding of the electrolyte. I

Manganese carbonate or oxide is added from time to time as it is needed to maintain an excess in the mixing tank. If manganese carbonate is used. it can be produced by the addition of soluble carbonate, such as sodium carbonate, sodium bicarbonate, or ammonium carbonate, to solutions of manganese sulphate or manganese chloride. The manganese carbonate, either known methods of leaching manganese bearing ores .or manganese compounds. The mineral rhodochrosite (MnCOa) can be ground to suitable fineness and added directly to the mixing tank if it is available in sufllcient quantity and If ammonium carbonate is employed as the precipitating agent for producing manganese carbonate from pregnant manganese sulphate pounds; that manganese of relatively low purity L flows to a settling tank or filter D in which the solution, the other reaction product is ammonium sulphate, which remains in solution. Ammonium carbonate can be regenerated from the ammonium sulphate solution by at least three methods: a

(1) The ammonium sulphate is crystallized by evaporation, calcium carbonate in some form is added, and by dry distillation ammonium car-, bonate is evolved and condensed;

(2) Finely powdered limestone or chalk is added to the ammonium sulphate solution, the mixture is distilled at slightly lower temperature than the boiling point of water and the distillate, which in a solution of ammonium carbonate, is condensed;

(3) Lime is added to the ammonium sulphate solution, the mixture is distilled at approximately 60 C. and ammonia gas is evolved. The ammonia gas can be combined with carbon dioxide produced by well known processes to form ammonium carbonate.

In the apparatus constructed to carry the preceding process into effect, the electrolyte contained approximately 80 grams of manganese sulphate, approximately 150 grams of ammonium sulphate, and approximately 1 gram of ammonium su'lphite per liter of water. A rate of flow was maintained which required four hours to complete the cycle. Sulphur dioxide gas was added continuously to the electrolyte at the entrance to the catholyte compartments. Diaphragms were of commercial storage-battery wood separators. The anodes were of lead. The cathode was of low-carbon steel with a polished surface. Manganese carbonate, produced by precipitation and filtration from two-normal manganese sulphate solution with ammonium carbonate, was added from time to time to the mix ing tank. Electrolysis was maintained for a total of 48 hours at atmospheres between 20 and 25 C. at a cathode current density of 33 amperes per square foot and an electrode potential of 5 volts. With this set up a compact, coherent metallic deposit of manganese containing less than 0.2 percent impurities was obtained. The deposit was brittle and easily removable from the sheet-steel cathode. The over-all current efliciency was 55 percent. The current efficiency during the last 9 hours of electrolysis was 64 per-. cent. The power consumption was at the rate of 4.1 kilowatt hours per pound of manganese produced.

In the light of the preceding disclosure it will be evident this invention provides a method for the electrolytical extraction of metallic manganese from aqueous solutions, which is industrially feasible, highly efficient and which yields praciically pure metallic manganese deposits, the latter exceeding in weight any heretofore obtained.

Having described my invention, what I claim as new and wish to secure by Letters Patent is:

l. A process for the electro-deposition of high purity manganese consisting in introducing an electrolyte into an electrolyticalcell, the electrolyte being composed of an aqueous solution of ammonium and manganese salts, the ammonium sait beingselected from the group consisting of ammonium sulphate and ammonium chloride, the manganese salt being selected from the group consisting of manganese sulphate and-manganese chloride, the solution having a minimum concentration of 0.5 gram per liter of manganese a concentration ratio of ammonia to manganese in solution which is approximately or greater than 17 to 55 by actual weight and containing a sulphite ion to the limit of its solubility and then electrolyzing with a minimum cathode current density of 10 amperes per square foot.

2. A process including the steps of claim 1, wherein the conditions defined by said claim are maintained by the addition of sulphur dioxide gas and manganese carbonate to the electrolyte.

3. A process including the steps of claim 1,

'wherein the conditions defined by said claim are maintained by the addition of sulphurous acid,

and manganese carbonate to the electrolyte.

4. A process including the steps of claim 1, wherein the conditions defined by said claim are maintained by the addition of sulphur dioxide gas and manganese oxides to the electrolyte.

5. A process including the steps of claim 1, wherein the conditions defined by said claim are maintained by the addition of ammonium sulphite and manganese oxide to the electrolyte.

6. A process for the electro-deposition of high purity manganese consisting in introducing an electrolyte into an electrolytical cell, the electrolyte being composed of an aqueous solution of ammonium and manganese salts, the ammonium salt being selected from the group consisting of ammonium sulphate and. ammonium chloride, the manganese salt being selected from the group consisting of manganese sulphate and manganese chloride, the solution having a minimum concentration of 0.5 gram per liter of manganese, a concentration ratio of ammonia to manganese in solution which is approximately or greater than 17 to 55 by actual we ght and con-' taining sulphite ion to the limit of its solubility,

electrolyzing with a minimum cathode current,

density of 10 amperes'per square foot and maintaining the hydrogen ion concentration of that part of the electrolyte near the cathode at a lower value than the hydrogen ion concentration of the electrolyte near the anode.-

7. A cyclic process for the electro-deposition of high purity manganese consisting in introducing an electrolyte into the cathode compartment of an electrolytical cell, the electrolyte being composed of an aqueous solution of ammonium and manganese salts. the ammonium salt being selected from the group consisting of ammonium sulphate and ammonium chloride, the manganese salt being selected from the group consisting of manganese sulphate and manganese chloride, the solution having a minimum concentration of 0.5 gram per liter of manganese, the concentration ratio ofammonia to manganese in solution being equal to or greater than 17 to by actual weight and containing sulphite ion to the limit of its solubility, electrolizlng with a minimum cathode current density of 10 amperes per square foot, while causing the electrolyte to circulate from the region near the cathode to the region near the anode, whereby the electrolyte near the cathode is maintained with a low hydrogen concentration, more suitable for metallic deposition and that part of the electrolyte near the anode is maintained at a higher hydrogen concentration, more suitable for react- .ing with manganese carbonate or manganese of an electrolytical cell, the electrolyte being composed of an aqueous solution of ammoniumand manganese salts, the ammonium salt being selected from the group consisting of ammonium sulphate and ammonium chloride, the mangafrom the region near the cathode to the region near the anode to maintain the hydrogen ion concentration of that part of the electrolyte near the cathode, of lower value than the hydrogen ion concentration of the electrolyte near the anode, circulating the spent electrolyte from' the anode compartment to a rejuvenating chamber wherein it is treated with a manganesebearing compound and restored to its initial strength and then circulating the replenished electrolyte to a settling chamber to remove excess manganese-bearing compound and thence to the cathode compartment into which it is reintroduced with the addition of a sulphite ion.

9. A cyclic process for the electro-deposition of high purity manganese consisting in introducing an electrolyte into the cathode compartment oi an electrolytical cell, the electrolyte be ing composed of an aqueous solution of ammonium and manganese salts, the ammonium salt being selected from the group consisting of ammonium sulphate and ammonium chloride, the manganese salt being selected from the group consisting of manganese sulphate and manganese chloride, the solution having a minimum concentration of 0.5 gram per. liter of manganese, the concentration ratio of ammonia to manganese in solution being equal to or greater than 17 to 55 by actual weight, electrolyzing with a minimum cathode current density of .amperes per square foot and causing the electrolyte to ilow from the region near the cathode to the region near the anode to maintain the hydrogen ion concentration of that part of the electrolyte near the cathode of lower value than the hydrogen ion concentration of the electrolyte near the anode, circulating the spent electrolyte from the anode compartment to a rejuvenating chamber wherein it is treated with a manganese-bearing compoundand restored to its initial strength and then circulating'the replenished electrolyte to asettling chamber to remove excess manga nese-bearing compound and thence to the cathode compartment into which it is reintroduced with the addition of sulphur dioxide.

10. A cyclic process for the electro-deposition of high purity manganese consisting in introducing an electrolyte into the cathode compartment of an electrolytical cell, the electrolyte being composed of an aqueous solution-of ammonium and manganese salts, the ammonium salt being selected from the group consisting of ammonium sulphate and ammonium chloride, the manganese salt being selected from the group consisting of manganese sulphate and manganese chloride, the solution having a minimum concentration of 0.5 gram per liter oi manganese, the concentration ratio of ammonia to manganese in solution being equal to or greater than 17 to 55 by actual weight, electrolizing with .'a minimum cathode current density of 10 amperes per square foot and causing the electrolyte to flow from the region near the cathode to that near the anode whereby to maintain the hydrogen ion concentration of that part of the electrolyte near the cathode at a lower value than the hydrogen ion concentration of the electrolyte near the anode, circulating the spent electrolyte from the anode compartment to a rejuvenating chamber wherein it is treated with-a manganese carbonate and restored to its original strength, then directing the electrolyte to a settling chamber to remove excess manganese carbonate and thence tothe cathode compartment into which (it is reintroduced with the addition of a'sulphite ion. I 11. A cyclic process for the elec ors-deposition of high purity manganese consisting in introducing an electrolyte into the cathode compartment oi an electrolytical cell, the electrolyte being composed of an aqueous solutionoi' ammonium and. manganese salts, the ammonium salt being selected from the group consisting of ammonium sulphate and ammonium chloride, the manganese salt being selected from the group consisting of -manganese sulphate and manganese chloride, the solution having a min.- imum concentration of 0.5-gram per liter of manganese, the concentration ratio of ammonia to manganese in solution being equal to or greater than 17 to 55 by-actual weight, causing the electrolyte to flow from the region near the cathode to that near the anode whereby to maintain the hydrogen ion concentration of that part of the electrolytenear the cathode at a lower value I than the hydrogen ion concentration of the elec trolyte near the anode, circulating the spent electrolyte from the anode compartment to a rejuvenating chamber wherein it is treated with a manganesebearing compound to restore its original strength and then directing the electrolyte to a settling chamber to remove excess manganese-bearing compound and thence to the cathode compartment into which it is introduced with the addition of a sulphite ion, the rate of flow of the electrolyte being regulated and its volume adjusted so that ample time will be allowed for the reaction between the manganese-bearing compound and the-partially spent electrolyte containing free sulphuric acid.

12. A process including the steps of claim 1.

wherein the conditions defined by said claim are maintained by the addition of ammonium sulphite and manganese carbonate to the electrolyte.

13. A process including the steps of claim 1, wherein the conditions defined by said claim are maintained by the addition of sulphurous acid and manganese oxides to the electrolyte.

STEPHEN M. 'sHEL'roN. 

